Kling David E, Cavicchio Amanda J, Sollinger Christina A, Madoff Lawrence C, Schnitzer Jay J, Kinane Thomas B
Laboratory of Developmental Immunology, Department of Pediatrics, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, GRJ 1402, Boston, MA 02114, USA.
Microb Pathog. 2009 Jan;46(1):43-52. doi: 10.1016/j.micpath.2008.10.009. Epub 2008 Oct 26.
Group B Streptococcus (GBS) is a Gram-positive bacterium that causes sepsis and meningitis in neonates and infants. Although several GBS-associated virulence factors have been described, the mechanisms of GBS invasive disease are not well understood. To characterize additional virulence factors, a novel in vitro infection assay was developed using rat fetal lung explants. However, application of GBS to the system induced rapid lung tissue destruction associated with increased media acidity. Since lactic acid produced by other streptococci is an important virulence factor, we hypothesized that lactic acid contributed to the virulence of GBS. Spent growth media and neutralized-spent media were applied to explants and results indicated that neutralization of the media completely protected the tissue from degradation. These results were verified using multiple viability assays and with transformed cell lines. Furthermore, comparable spent media from Escherichia coli did not induce tissue cytotoxicity, suggesting that GBS produces organic acids in excess of other potential bacterial pathogens. Analysis of the spent media indicated that l-lactate levels reached approximately 70 mM, indicating that lactic acid is a major constituent of the metabolic acid produced by GBS. Treatment of explants with lactic acid alone produced dose-dependent tissue degradation, indicating that lactic acid is independently sufficient to induce target-tissue cytotoxicity. Finally, both spent media and 23.6 mM lactic acid produced dramatic tissue autofluorescence; the basis for this is currently unknown. These studies demonstrate that GBS-produced lactic acid is a potential virulence factor and may contribute to GBS invasive disease.
B族链球菌（GBS）是一种革兰氏阳性细菌，可导致新生儿和婴儿败血症和脑膜炎。尽管已经描述了几种与GBS相关的毒力因子，但GBS侵袭性疾病的机制尚未完全了解。为了鉴定其他毒力因子，利用大鼠胎儿肺外植体开发了一种新型体外感染试验。然而，将GBS应用于该系统会导致肺组织迅速破坏，并伴有培养基酸度增加。由于其他链球菌产生的乳酸是一种重要的毒力因子，我们推测乳酸有助于GBS的毒力。将用过的生长培养基和中和后的用过的培养基应用于外植体，结果表明培养基的中和完全保护了组织不被降解。这些结果通过多种活力测定法和转化细胞系得到了验证。此外，来自大肠杆菌的类似用过的培养基不会诱导组织细胞毒性，这表明GBS产生的有机酸超过了其他潜在的细菌病原体。对用过的培养基的分析表明，L-乳酸水平达到约70 mM，这表明乳酸是GBS产生的代谢酸的主要成分。单独用乳酸处理外植体会产生剂量依赖性的组织降解，这表明乳酸足以独立诱导靶组织细胞毒性。最后，用过的培养基和23.6 mM乳酸都会产生显著的组织自发荧光；其原因目前尚不清楚。这些研究表明，GBS产生的乳酸是一种潜在的毒力因子，可能导致GBS侵袭性疾病。
